Hydraulic system with energy regeneration

ABSTRACT

A hydraulic system includes a tank for hydraulic fluid, a supply line connected to the tank and a plurality of hydraulic functions connected to the supply line. Each hydraulic function includes an actuator that is connectable to a load and that has a first side and a second side. Each function includes a first control valve connected to the first side and a second control valve connected to the second side. Each function also has an independent tank line, and the first and second control valves are connected to both the supply line and the independent tank line. A third control valve is connected between the independent tank line and the tank, and a check valve is connected between the supply line and the independent tank line.

TECHNICAL FIELD

The present invention relates to hydraulic system, and more particularlyto a hydraulic system used to raise and lower a load.

BACKGROUND OF THE INVENTION

Hydraulic systems are commonly used in heavy machinery, such asearth-moving machines or agricultural equipment. Generally, hydraulicsystems use valves to control circulation of pressurized fluid through anetwork of lines. Selective operation of the valves controls the fluidpressure in hydraulic actuators, such as cylinders, to carry out variousfunctions on one or more loads.

Currently-known hydraulic systems often waste energy when lowering aload. For example, when gravity lowers a load during a first operation,the fluid expelled from a non-operating portion of an actuator (e.g., acylinder) may be drained directly to a tank. To provide pressurizedfluid for another operation (e.g., operating an arm at the end of theload, raising the load at a later time, etc.), a pump must consumeadditional energy because when the fluid is expelled, the potentialenergy in the drained fluid from the first operation is lost to heat andtherefore is not available for use by any other operation. Thus, thesecond operation must draw energy from the engine to increase the fluidpressure to an operational level.

Some hydraulic systems capture energy by routing expelled fluid toanother portion of the actuator or even to different actuator. Thecaptured energy can reduce the amount of additional energy needed topressurize the fluid for another operation and may also reduce the cycletime of the hydraulic system. Re-routing fluid to use the potential orstored energy in the fluid is often referred to as “regeneration.”

Some regeneration systems can only recycle fluid from one cylinderchamber to another or store fluid under pressure in an accumulator. Thislimits the applications in which energy regeneration can be used. Othersystems allow regeneration among multiple functions, but regeneration inone function may negatively affect another function because the tanklines for different functions are interconnected. For example, raisingthe tank line pressure in one function raises the tank line pressure inthe entire system, thereby reducing the ability to overcome externalforces acting on the cylinder. If the other functions attempt to movetheir respective loads in the opposite direction of this external force,the system efficiency decreases because the supply pressure mustovercome both forces (e.g., gravitational forces) on the load and theraised tank pressure to move the load in the desired manner.

There is a desire for a multi-function hydraulic system that isolatesthe functions from each other yet still allows cross-functionregeneration when desired.

SUMMARY

A hydraulic system according to one aspect includes a tank for hydraulicfluid, a supply line connected to the tank, and a plurality of hydraulicfunctions connected to the supply line. Each hydraulic function includesan actuator that is connectable to a load. The actuator itself has afirst side and a second side. Each function includes a first controlvalve connected to the first side and a second control valve connectedto the second side. Each function also has an independent tank line, andthe first and second control valves are connected to both the supplyline and the independent tank line. A third control valve is connectedbetween the independent tank line and the tank, and a check valve isconnected between the supply line and the independent tank line.

A hydraulic system according to another aspect includes a tank forhydraulic fluid, a controller, a supply line connected to the tank, apump connected between the tank and the supply line, a plurality ofloads, and a plurality of hydraulic functions, where each hydraulicfunction is connected to one of the loads and the supply line. Eachhydraulic function includes a cylinder and a piston disposed within thecylinder. The piston is connected to the load and divides the pistoninto a rod side and a head side. Each hydraulic function also includes afirst operated control valve connected to the rod side and responsive toa first signal from the controller and a second control valve connectedto the head side and responsive to a second signal from the controller.Each function also includes an independent tank line, and the first andsecond control valves are connected to the supply line and theindependent tank line. A third control valve is connected between theindependent tank line and the tank, and a pressure-operated check valveis connected between the supply line and the independent tank line. Eachfunction also includes three pressure sensors to monitor pressure at therod side of the cylinder, at the head side of the cylinder, and in theindependent tank line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a hydraulic circuit according to one embodimentof the invention;

FIG. 2 is a schematic of a hydraulic circuit according to anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic of a hydraulic system 10 according to oneembodiment of the invention. For illustrative purposes only, the system10 shown in FIG. 1 has three separate functions 12, 14, 16. However, itshould be understood that the system 10 can contain any number offunctions without departing from the scope of the invention.

The functions 12, 14, 16 are linked together by a shared supply line 18that supplies hydraulic fluid from a tank 20 to the functions 12, 14, 16via a pump 22. A supply line sensor 24 may be included to monitor fluidpressure in the supply line 18.

Each function 12, 14, 16 has a corresponding actuator, such as acylinder 26, 28, containing a piston 32, 34, 36 that drives a load 38,40, 42. Note that other hydraulic actuators may be used in the system10. Each function 12, 14, 16 may carry out a different operationcorresponding to the particular load 38, 40, 42. For example, on anexcavator, load 38 may be a bucket, load 40 may be a boom, and load 42may be an arm. Other loads, load combinations, and/or operations mayalso be used in the system 10. Each function 12, 14, 16 also has anassociated independent tank line 43, 44, 45 that acts as a separate,parallel link between each function 12, 14, 16 and the tank 20. Thus,each function 12, 14, 16 shares a connection to the tank 20 via thesupply line 18 and also has its own, independent connection to the tank20 via its corresponding independent tank line 43, 44, 45.

For simplicity, the details of the functions 12, 14, 16 will now bedescribed with respect to function 12 only because the other functions14, 16 have the same internal circuit structure. The piston 32 dividesthe cylinder 26 into a rod side 26 a and a head side 26 b. Each side 26a, 26 b is a fluid chamber, and the fluid pressure in each side 26 a, 26b controls the operation of the load. Fluid flow to and from thecylinder 26 can be controlled proportional control valves 50, 52. In oneaspect of the system, the proportional control valves aresolenoid-controlled, but any proportional control valve can be used inthe system as well.

In one embodiment, a first proportional control valve 50 controls fluidflow to and from the rod chamber 26 a and a second proportional controlvalve 52 controls fluid flow to and from the head chamber 26 b. Thefirst and second proportional control valves 50, 52 are operable to beconnected to the supply line 18 or the independent tank line 43 In oneaspect of the system, the first and second control valves 50, 52 operateaccording to one of three scenarios: (1) one control valve 50, 52 isconnected to the supply line 18 and the other control valve 50, 52 isconnected to the tank 20, (2) both control valves 50, 52 are open to thetank, and (3) both control valves 50, 52 are open to the supply line 18.A first pressure gauge 54 may monitor the pressure at the rod side 26 aof the cylinder 26, and a second pressure gauge 56 may monitor thepressure at the head side 26 b of the cylinder 26.

A third proportional control valve 58 may control fluid flow from theindependent tank line 43 to the tank 20. In other words, the thirdcontrol valve 58 controls the fluid pressure in the independent tankline 43. A third pressure gauge 59 may be disposed at the output of thethird proportional control valve 58 to monitor the fluid pressure at theindependent tank line 43. The control valves 50, 52, 58 may besolenoid-operated valves that respond according to input signals from acontroller 60.

The control valves 50, 52 regulate fluid flow between the supply line 18and the cylinder 26 based on signals from the controller 60. As can beseen in FIG. 1, the control valves 50, 52 for the cylinder 26 canreceive fluid from both the supply line 18 and the independent tank line43. A check valve 62 may control fluid flow from the independent thankline 43 to the supply line 18. In one embodiment, the check valve 62 isclosed when the pressure in the supply line 18 is higher than thepressure in the independent tank line 43 to prevent flow from the supplyline 18 to the independent tank line 43, and the check valve 62 is openwhen the pressure in the supply line 18 is equal to or lower than thepressure in the independent tank line 43 to allow free flow to thesupply line 18. The check valve 62 allows fluid to flow back to thesupply line 18 so that the fluid can be used for another function 14,16.

The controller 60 itself controls operation of the system 10 byreceiving input signals from the pressure sensors 24, 54, 56, 59 andother input devices (not shown) and outputting signals to actuatesolenoids in the control valves 50, 54, 58 to carry out a desiredfunction. The controller 60 also monitors the pressure sensors 24, 54,56, 59 to ensure the system 10 is properly operating.

As explained above, regeneration generally involves supplying fluidexhausted from one portion of the actuator 26 into another portion ofthe actuator 26 in a given function 12 or to an actuator 28 in adifferent function 14 altogether. Regeneration reduces or eliminates theamount of fluid that must be supplied from the tank 20 to the actuator26 to carry out a given function. This reduces the amount of energyneeded to pressurize the fluid and also reduces the time needed for thefluid to reach its operational pressure, therefore improving system 10performance. The examples below describe possible regeneration processesthat can be carried out by the system 10.

In one operation, one or more functions 12 may recirculate fluid fromone side of the actuator 26 to the other within a single function.Although the example below focuses on a single function that involvessending fluid from the head side 26 b of the cylinder 26 to the rod side26 a of the cylinder 26 for simplicity in explanation, the fluid may berecirculated in other directions and/or within other functions 14, 16without departing from the scope of the invention. This operationgenerally corresponds to known recirculation functions.

Note that in one aspect of the system, the check valve 62 does not playa role in single-function regeneration because the check valve 62 isused to isolate the functions 12, 14, 16 from each other. Sincesingle-function regeneration focuses on a single function, there is noneed for the check valve 62 to isolate the functions.

To initially raise the load 38, the pump 22 increases the fluid pressurein the supply line 18, and the second control valve 52 is adjusted(e.g., via control of the solenoid current by the controller 60) tocontrol the fluid velocity though the valve 52. This fluid velocitycontrols the velocity at which the load is raised 38. The first controlvalve 50 is opened to minimize fluid flow restriction back to the tank20. The third control valve 58 is completely open to minimize thepressure drop across the valve 58 and allow fluid in the rod side 26 ato drain easily into the tank 20 without creating any fluid pressurethat could fight against the pressure buildup in the head side 26 bneeded to raise the load 38.

More particularly, the first control valve 50 is connected to theindependent tank line 43 and the second control valve 52 and connectedto the supply line 18. The fluid pressure in the supply line 18 throughthe second control valve 52 causes the head side 26 b of the cylinder 26to fill with pressurized fluid, actuating the piston 32 and forcingfluid out of the rod side 26 a back through the first control valve 50into the tank 20.

To lower the load 38 and recirculate the fluid within the function 12,the controller 60 adjusts the solenoid currents to the first and secondcontrol valves 50, 52 so they are both closed to the supply line 18 andboth connected to the independent tank line 43. The third control valve58 is restricted to generate pressure in the independent tank line 43and force some fluid to flow back to the rod side 26 a. Connecting thecontrol valves 50, 52 to the independent tank line 43 and restrictingthe third control valve 58 redirects fluid from the head side 26 b tothe rod side 26 a while still allowing excess fluid to drain into thetank 20.

When the load 38 drops (e.g., when gravity pulls the load downward), thepiston 32 lowers, forcing fluid out of the head side 26 b. The secondcontrol valve 52 may be metered, if desired, to control the rate atwhich fluid drains from the head side 26 b, thereby controlling the rateat which the load 38 lowers. Since the control valves 50, 52, 58restrict fluid from flowing to the tank 20, the fluid from the head side26 b creates a pressure differential that pushes fluid through thesecond control valve 52, through the independent tank line 43, andthrough the first control valve 50 into the rod side 26 a. In otherwords, the fluid exhausted from the head side 26 b is recirculated andsent to the rod side 26 a instead of drained to the tank 20, therebyallowing the potential energy to be used to fill the rod side 26 a.

In another operation, cross-functional regeneration may be desired,allowing energy captured from lowering one load 38 to be used to raiseor otherwise operate one or more other loads 40, 42 in the system 10. Todo this, the first control valve 50 is opened to connect the rod side 26a of the cylinder 26 to the independent tank line 43 and the secondcontrol valve 52 is opened to connect the head side 26 b to theindependent tank line 43. The third control valve 58 is closed orpartially closed to control the pressure in the independent tank line 43at a desired level.

When fluid exhausts out of the head side 26 b, it flows though the opensecond control valve 52 to the independent tank line 43. If the pressurein the supply line 18 is lower than the pressure in the independent tankline 43, the check valve 62 opens to connect the independent tank line43 with the supply line 18. This allows the exhausted fluid to flow intothe supply line 18 and raise the supply line 18 pressure. The increasedsupply line 18 pressure makes the energy from the exhausted fluidavailable to power loads in any of the other functions 14, 16 (assumingthe load pressures in functions 14 and 16 are lower than the loadpressure in function 12) because the supply line 18 is connected to allof the functions 12, 14, 16. Thus, loads 40 and 42 can be raised orotherwise operated using the increased fluid pressure in the supply line18 created by the lowered load 38. If the supply line 18 already hassufficient operating pressure, the pump 22 does not need to be operatedto raise the loads 40, 42.

In yet another operation, fluid is recirculated in one function whilethe pump is activated to lift loads in other functions. This is possiblein the inventive system 10 because the independent tank lines 43, 44, 45allow each function 12, 14, 16 to operate independently, with its ownassociated fluid pressures, without affecting the operation of the otherfunctions 12, 14, 16 in the system 10. More particularly, in oneexample, fluid may recirculate in function 12 in the manner describedabove. The check valve 62 isolates the function 12 from the supply line18 and the other functions 14, 16. The check valves in the otherfunctions 14, 16 isolate their corresponding functions 14, 16 as well.

With respect to function 12, when the pressure in the supply line 18 ishigher than the pressure in the independent tank line 43, the checkvalve 62 closes to isolate the function 12 from the supply line 18. Asin the previous example, recirculation pressure may be generated whenfluid exhausts from the head side 26 b. If the third control valve 58operates so that the pressure in the independent tank line 43 is thesame as or greater than the supply line 18 pressure, the check valveopens and connects the independent tank line 43 to the supply line 18.Once this connection occurs, function 12 is connected to the otherfunctions, and the increased supply line pressure may power the otherfunctions 14, 16 or cross-functional regeneration.

If a given function does not need additional fluid flow however, thecheck valves 62 in each function 12, 14, 16 can continue to isolate theindependent tank line 43, 44, 45 for each function from the supply line18. For example, to lower the first load 38 and raise one or both of theother loads 40, 42, it is desirable to drain the independent tank linecorresponding to the load(s) to be lifted 40, 42 during a liftingoperation. Draining ensures that the fluid pressure in the independenttank line(s) 44, 45 is minimized, which optimizes energy efficiency andgenerates maximum load lifting capacity. Draining the independent tankline 44, 45 may be achieved by fully opening the third control valve 58of functions 14 and 16.

When load 38 is lowered, the third control valve 58 of function 12 isrestricted to raise the pressure at the independent tank line 43 and thesupply line 18. However, since the third control valves 58 in the otherfunctions 14, 16 are still fully open, the pressure in the independenttank lines 44, 45 is lower than the pressure in independent tank line43, allowing cross-functional regeneration to occur.

Thus, the independent tank lines 43, 44, 45, check valves 62, and thirdcontrol valves 58 in each function 12, 14, 16 allow selective connectionand isolation of the functions 12, 14, 16 from each other. Moreparticularly, the check valve 62 connects or isolates a given function12, 14, 16 to or from the supply line 18, while the third control valve58 controls the pressure in the independent tank line 43, 44, 45 to openor close the check valve 62 depending on the relative pressures of thesupply line 18 and the independent tank line 43, 44, 45. The system 10therefore can provide cross-function regeneration to reuse energy thatwould ordinarily be wasted.

FIG. 2 illustrates an alternative embodiment of the hydraulic system 10.In this embodiment, the third control valves 58 in each function 12, 14,16 are replaced with pressure-controlled check valves 70. The checkvalve 70 maintains pressure in the independent tank line 43 at a singlepredetermined level. based on the difference between the pressure in thesupply line 18 and the pressure in the tank 20.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

What is claimed is:
 1. A hydraulic system, comprising: a tank forhydraulic fluid; a supply line connected to the tank; a plurality ofhydraulic functions connected to the supply line, each hydraulicfunction including an actuator that is connectable to a load, whereinthe actuator has a first side and a second side; a first control valveconnected to the first side, a second control valve connected to thesecond side, an independent tank line, wherein the first and secondcontrol valves are connected to the supply line and the independent tankline, a third control valve connected between the independent tank lineand the tank, and a check valve connected between the supply line andthe independent tank line.
 2. The hydraulic system of claim 1, whereinthe actuator is a cylinder, the first side is a rod side and the secondside is a head side, and wherein the system further comprises a pistondisposed within the cylinder and separating the rod side and the headside.
 3. The hydraulic system of claim 1, further comprising acontroller, and wherein at least one of the first and second controlvalves are controlled by the controller.
 4. The hydraulic system ofclaim 4, wherein the first and second control valves aresolenoid-operated valves.
 5. The hydraulic system of claim 4, whereinthe third control valve is a solenoid-operated valve controlled by thecontroller.
 6. The hydraulic system of claim 4, wherein the thirdcontrol valve is a pressure-controlled valve.
 7. The hydraulic system ofclaim 1, wherein the check valve is a pressure-operated valve.
 8. Thesystem of claim 1, further comprising a pump connected between the tankand the supply line.
 9. The system of claim 1, further comprising afirst pressure sensor that monitors pressure at the first side of theactuator and a second pressure sensor that monitors pressure at thesecond side of the actuator.
 10. A hydraulic system, comprising: a tankfor hydraulic fluid; a controller; a supply line connected to the tank;a pump connected between the tank and the supply line; a plurality ofloads; and a plurality of hydraulic functions, each hydraulic functionconnected to one of said plurality of loads and connected to the supplyline, wherein each hydraulic function includes a cylinder and a pistondisposed within the cylinder, wherein the piston is connected to theload and divides the piston into a rod side and a head side, a firstoperated control valve connected to the rod side and responsive to afirst signal from the controller, a second control valve connected tothe head side and responsive to a second signal from the controller, anindependent tank line, wherein the first and second control valves areconnected to the supply line and the independent tank line, a thirdcontrol valve connected between the independent tank line and the tank,a pressure-operated check valve connected between the supply line andthe independent tank line, a first pressure sensor that monitorspressure at the rod side of the cylinder, a second pressure sensor thatmonitors pressure at the head side of the cylinder, and a third pressuresensor that monitors pressure in the independent tank line.
 11. Thehydraulic system of claim 10, further comprising a controller, andwherein at the first and second control valves are solenoid-operatedvalves.
 12. The hydraulic system of claim 10, wherein the third controlvalve is a solenoid-operated valve controlled by the controller.
 13. Thehydraulic system of claim 10, wherein the third control valve is apressure-operated valve.